Grid active filter structure and its application - Power Circuit - Circuit Diagram

Full Range MOS Power IC

Filter 18.432M

In the realm of non-linear AC networks, active filtering has emerged as a well-established technology for mitigating harmonics and providing reactive power compensation. This paper offers an extensive overview of the structural features and applications of active filters within AC power grids while forecasting the future trajectory of active filter technology. Key descriptors include active filter, harmonic, reactive power compensation, and passive filter. Abstract: Active power filtering in electrical systems has become a refined approach for addressing harmonic issues and reactive power compensation in non-linear loads. This paper provides a comprehensive review of various Active Power Filter (APF) configurations, aiming to offer readers a clear understanding of the current state of APF topology technology and the potential for broader APF application. Keywords: active power filters, harmonic, reactive power compensation, passive filter. 1. Introduction: As power electronics technology continues to evolve rapidly, the integration of large-scale power electronic devices into power systems has surged. These advancements enhance industrial automation levels and efficiency, yet they introduce significant challenges. Non-linear loads, often employing traditional phase-controlled rectifier technology, generate high harmonics and operate at low power factors, posing serious threats to the stability and quality of the power grid. Traditionally, harmonic suppression and reactive power compensation involve connecting passive filters in parallel with non-linear loads to create low-resistance paths for harmonics and supply necessary reactive power. Passive filters (PFs) boast simplicity, ease of use, established technology, and affordability. However, they also have notable drawbacks: 1) their performance is highly dependent on the grid and load, resulting in suboptimal filtering outcomes; 2) they risk causing series or parallel resonance with the grid; 3) they can only compensate fixed reactive power, failing to dynamically adjust to fluctuating demands; and 4) require bulky energy storage components. Active Power Filters (APFs), on the other hand, address these limitations effectively. Unlike passive filters, APFs exhibit minimal sensitivity to grid and load variations, eliminating the risks of resonance while enabling dynamic compensation for both frequency and magnitude of harmonics and reactive power. They simultaneously compensate for harmonics and reactive power, allowing continuous adjustment of reactive power, and can handle either task independently or manage multiple harmonic and reactive sources together. Furthermore, APFs require no bulky energy storage components when compensating reactive power, and their harmonic compensation energy storage requirements remain manageable. This paper delves into the fundamental principles and structural attributes of active filters, explores their developmental status and applications, and ultimately speculates on their future trajectory. 2. Active Filter Principles and Structure: An active filter comprises switching devices and passive energy storage components like inductors and capacitors. It operates through two main circuits: the command current calculation circuit and the compensation current generation circuit. The basic operational principle involves detecting the load current (or voltage), computing a compensation current command signal, and generating a compensation current via the controller to neutralize the harmonic current in the load. This process restores the grid current to a pure sinusoidal waveform and generates a fundamental reactive current for reactive power compensation. Figure 1 illustrates the structure of an active filter. 3. Active Filter Topologies and Applications: Depending on how the active power filter connects to the grid, there are three primary system configurations: parallel, series, and hybrid types. 3.1 Parallel Active Filters: Typically, shunt active filters are utilized in three ways: standalone, combined with passive filters, and injecting current. 3.1.1 Standalone Parallel APF Configuration: Shown in Figure 2, this represents the simplest form of an active filter. It generates a compensation current equal in magnitude but opposite in direction to the load harmonics, thereby purifying the supply-side current into a sine wave. Primarily designed for inductive current source loads, this setup remains the most widely implemented in industries. However, it requires high-voltage tolerance for switching elements due to direct grid voltage exposure. Additionally, when dealing with high load harmonic currents, the APF must have a substantial capacity, making it challenging to achieve both high compensation capacity and a wide compensation band.